user: implement mlibc as the libc, finally.

It's finally done..

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/include/mlibc/tests/rtld/search-order/libbar.c

@@ -0,0 +1,19 @@
+#include <assert.h>
+#include <dlfcn.h>
+
+#ifdef USE_HOST_LIBC
+#define LIBFOO "libnative-foo.so"
+#else
+#define LIBFOO "libfoo.so"
+#endif
+
+int foo(void);
+
+int bar(void) {
+	return foo();
+}
+
+[[gnu::constructor]] void init(void) {
+	void *libfoo = dlopen(LIBFOO, RTLD_LOCAL | RTLD_NOW);
+	assert(libfoo);
+}

user/include/mlibc/tests/rtld/search-order/libfoo.c

@@ -0,0 +1,3 @@
+int foo(void) {
+	return 0xCAFEBABE;
+}

user/include/mlibc/tests/rtld/search-order/meson.build

@@ -0,0 +1,32 @@
+# meson does not have native custom_target, so when cross compiling it gets
+# unhappy that we're trying to link a "host" library (which is actually built
+# for the build machine) to a build executable. This means we can't patchelf
+# native libraries if we want cross compilation to work.
+
+patchelf = find_program('patchelf', required: false)
+
+if patchelf.found()
+	# Overwrite LD_LIBRARY_PATH to make meson not fix our shenanigans
+	# Otherwise, meson's LD_LIBRARY_PATH makes this test useless because libfoo
+	# will be found through it instead of failing when libfoo is not found
+	test_env += ['LD_LIBRARY_PATH=']
+	test_native_env += ['LD_LIBRARY_PATH=']
+
+	libfoo = shared_library('foo', 'libfoo.c', link_args: test_additional_link_args)
+	libbar_unpatched = shared_library('bar-unpatched', 'libbar.c',
+		link_args: test_additional_link_args,
+		override_options: 'b_sanitize=none',
+		dependencies: libc_dep,
+		link_with: libfoo)
+	libbar = custom_target('patch-libbar',
+		command: [patchelf,
+			'--remove-rpath',
+			'--set-soname', 'libbar.so',
+			libbar_unpatched,
+			'--output', '@OUTPUT0@'],
+		output: ['libbar.so'],
+	)
+	test_link_with = [libbar, libfoo]
+else
+	test_skipped = true
+endif

user/include/mlibc/tests/rtld/search-order/test.c

@@ -0,0 +1,21 @@
+#include <assert.h>
+#include <dlfcn.h>
+
+#ifdef USE_HOST_LIBC
+#define LIBBAR "libnative-bar.so"
+#else
+#define LIBBAR "libbar.so"
+#endif
+
+int foo();
+int bar();
+
+int main() {
+	void *libbar = dlopen(LIBBAR, RTLD_LOCAL | RTLD_NOW);
+	assert(libbar);
+
+	assert(foo() == (int) 0xCAFEBABE);
+	assert(bar() == (int) 0xCAFEBABE);
+
+	return 0;
+}